The present invention relates to the control of an internal combustion engine. More specifically, the present invention relates to calibrating target wheels for speed, timing, and position sensing systems used in internal combustion engines.
Presently, automotive companies manufacture data or target wheels for use with speed sensors to detect the speed, timing, and position of an engine crankshaft and/or a camshaft. As is known in the art of four-cycle internal combustion engines (ICEs), position and timing between a crankshaft and a camshaft is very important for the application and synchronization of spark and fuel, as the camshaft actuates the intake and exhaust valves of an ICE. A camshaft may be used in an overhead valve (OHV) configuration where the valves are actuated via pushrods, or in an overhead cam (OHC) configuration where the valves are acted on directly by the camshaft. The camshaft is driven by the crankshaft through a 1:2 reduction (i.e., two rotations of the crankshaft equal one rotation of the camshaft) and the camshaft speed is one-half that of the crankshaft. The crankshaft and camshaft position, for engine control purposes, are measured at a small number of fixed points, and the number of such measurements may be determined by the number of cylinders in the ICE.
As previously described, engine control systems use the timing and position information supplied by a crankshaft and camshaft sensor for controlling the application of spark and fuel to the cylinders of an ICE. The position and timing (phase) of a first camshaft controlling exhaust valves for a cylinder and/or a second camshaft controlling intake valves for a cylinder in an overhead cam engine may be controlled relative to the crankshaft (piston position) to reduce emissions and improve fuel economy. Several cam-phasing devices (cam phasers) exist in today""s automotive market that require accurate position and timing information provided by the camshaft position sensor. The crankshaft and/or camshaft position sensor typically include a variable reluctance or Hall effect sensor positioned to sense the passage of a tooth, tab and/or slot on a target or data wheel coupled to the camshaft.
The target or data wheel used with present camshaft position sensors have a distribution of teeth, tabs and/or slots. The camshaft position sensor typically comprises a variable reluctance or Hall effect sensor positioned to sense the teeth on a target or data wheel coupled to the camshaft. The magnetic properties and material composition of the target wheel will vary where and when the sensor senses the teeth on a moving target wheel. This variation may cause problems in the feedback provided by the sensor. For example, two target wheels with identical footprints but made of different materials will have different magnetic and switching characteristics. Referring to FIG. 1, a sensor 18 is positioned to sense the teeth 40/41 of target wheel 23. For a first material, the sensor may switch at point A and for a second material the sensor 18 may switch at point B. The varying material compositions that happen during manufacturing processes even within the same xe2x80x9cbatchxe2x80x9d of target wheels produced in the same factory may lead to an inconsistency in sensing or switching. This difference in switching between point A and point B will adversely affect the ability to predict the switching position of the sensor 18 and program or calibrate the control of an ICE. Thus, there is a need to better determine the magnetic and switching characteristics for a target wheel to more accurately control an ICE.
The present invention comprises a target wheel calibration method and apparatus used to detect camshaft and crankshaft timing, position and speed for a four-cycle internal combustion engine (xe2x80x9cICE""xe2x80x9d). The present invention utilizes a method of detecting the position of a target wheel tooth (or teeth) at a known position relative to the crankshaft and camshaft. The method comprises zeroing/homing a cam phaser coupled to the target wheel and camshaft and then rotating the crankshaft through two revolutions (thereby rotating the camshaft one revolution) to determine where the teeth of the target wheel switch the sensor. The switching time and position of the teeth of the target wheel on the camshaft are referenced to the target wheel pulse train of the crankshaft. The switching position of the target wheel on the camshaft is thus xe2x80x9cknownxe2x80x9d with respect to the position of the crankshaft and corresponding cylinder events. This position and timing information is stored and referenced by a controller to control the functions of the ICE.